OMD's position as the retained media agency on Yahoo!'s media planning and buying account is unaffected by the appointment. OgilvyOne will handle creative for the launch.
Carat has been chosen to handle communications stra-tegy, planning and buying across all media for Yahoo! Answers in the UK. The Aegis-owned agency will create a launch campaign incorporating online, radio and press activity.
The social search product allows people anywhere in the world to answer questions posed by other users.
Microsoft's online service, MSN, is currently preparing to launch its own product to rival Answers.
Greg Grant, the marketing director, at Yahoo! UK and Ireland, said: "The launch of Yahoo! Answers is integral to our vision of the future of search.
We believe Carat is the right media agency to support this high-profile campaign." He added that Carat's buying efficacy was instrumental in the appointment.
The move comes as media owners take an interest in the increasing popularity of social network sites. Last month, NBC Universal acquired the women's site iVillage for $600 million and News Corporation paid $580 million in 2005 for MySpace.com.